Abstract

Spatial and temporal relationships between climate, tectonics, and sea level have a primary control on sediment transport, storage, and deposition in onshore and offshore depositional environments. Although many simplistic models have tried to predict onshore system behavior and sediment partitioning between onshore and offshore depositional environments in response to changes in these boundary conditions, the alluvial response to changes in external forcings coupled with autogenic processes can be highly complex and unpredictable.

The Golo source-to-sink system, on the eastern margin of the island of Corsica in the Mediterranean Sea, provides an ideal laboratory to study sediment partitioning in both onshore and offshore realms. The terrestrial part of the system consists of the Golo River, which debouches onto a narrow shelf (~ 10 km), which in turn passes into a narrow (~ 45 km) confined basin known as the Corsica Trough, dominated by submarine fan deposits. Estimates on timing of late Quaternary fluvial aggradation are compared with timing of sediment storage on the shelf and on the basin-floor fan. The results indicate that onshore deposition and storage of sediment in the fluvial system may occur both during sea-level highstand, transgression, and lowstand. Volume calculations from the alluvial record show that onshore storage is relatively low (~ 13%) relative to the overall sediment budget. Comparing estimated deposition rates with a sediment prediction model further suggests that deep-sea fan sedimentation rates at times may be up to 50% higher or 25% lower than what is being supplied by the river, indicating temporary storage and release of sediment on the shelf. On average, however, there is good agreement between predicted and calculated sediment volumes in the Golo system. The study demonstrates the value of investigating the entire source-to-sink system in order to obtain a comprehensive understanding of sediment dispersal between onshore and offshore depositional environments over 10⁴ year timescales.

Observations suggest that alternating periods of aggradation and degradation of the Golo River are controlled by system thresholds controlled from within the catchment. Comparison with climate proxy data and timing of major alluviation events elsewhere in the Mediterranean region supports the notion that each source-to-sink system has a unique threshold that must be exceeded to induce regional aggradation and subsequent terrace formation. The same is also inferred for timing of sediment dispersal to the deep-sea environment. In addition, preservation of onshore sediment is controlled by local factors such as uplift rate and its impact on the aggradational response. It is, therefore, expected that the onshore record may be diachronous on local, regional, and global scales, making detailed correlation difficult except for the most extreme events. Finally, stream incision rates appear to be one to two orders of magnitude higher than regional hinterland denudation rates, indicating that the Golo system is characterized by increasing landscape relief.